Water-absorbent resin composition

ABSTRACT

A water-absorbent resin composition having superior gel stability which comprises a water-absorbent resin, at least one oxygen-containing reducing inorganic salt and, optionally, at least one organic antioxidant.

FIELD OF THE INVENTION

The present invention relates to a water-absorbent resin composition.More particularly, it relates to a water-absorbent resin compositionhaving an improved stability to body fluids such as urine, catamenialblood, secretions and the like, and further relates to a water-absorbentresin composition having an improved stability to an aqueous solutioncontaining an electrolyte in addition to an improved stability to bodyfluids.

BACKGROUND OF THE INVENTION

Recently, various water-absorbent resins have been developed (forexample, see U.S. Pat. No. 4,340,706, U.S. Pat. No. 4,093,776, U.S. Pat.No. 4,459,396, U.S. Pat. No. 3,980,663 and U.S. Pat. No. 4,552,938) andhave been extensively used in various water-absorbent articles such asdiaper, menstrual articles and the like. Thereby, properties ofwater-absorbent articles are improved. For example, liquid retentioncharacteristics are improved and liquid leak is diminished. Further, acomfortable feeling in wearing water-absorbent article which hasabsorbed body fluids is achieved. Accordingly, such a water-absorbentarticle tends to be kept on for a longer period of time.

On the other hand, it has been found that a gel resulted from absorptionof fluids such as urine, catamenial blood, secretions and the like by awater-absorbent article is crumbled to be out of shape because, ingeneral, a water-absorbent resin of the gel is decomposed by the bodyfluids with time. Accordingly, as a period of time for keeping awater-absorbent article on becomes larger, liquid retentioncharacteristics of the article are lowered, which results in increase inliquid leak, impairment of feeling in wearing the article and the like.In view of this, it is required to develop a water-absorbent resin whichhas an improved gel stability to the body fluids.

As a means for improving a gel stability, for example, increase incrosslinking density of a water-absorbent resin may be employed.However, as crosslinking density becomes higher, a water-absorptioncapacity becomes lower and therefore it is necessary to increase anamount of the resin to be used. This is less economical and causes sucha disadvantage that properties of a water-absorbent article areadversely affected.

OBJECTS OF THE INVENTION

Under these circumstances, the present inventors have studiedintensively to obtain a water-absorbent resin having an improved gelstability to the body fluids. As the result, it has been found that agel stability of water-absorbent resin to the body fluids can besufficiently improved without the above disadvantages by incorporationwith an oxygen-containing reducing inorganic salt. Further, it has beenfound that, in addition to a gel stability to the body fluids, a gelstability of a water-absorbent resin to an aqueous solution containingan electrolyte can be also sufficiently improved with maintaining itshigh water-absorption capacity by incorporation with an organicantioxidant together with the oxygen-containing reducing inorganic salt.

That is, one object of the present invention is to provide awater-absorbent resin composition having an improved gel stability tothe body fluids which is suitable for water-absorbent articles.

Another object of the present invention is to provide a water-absorbentresin composition having an improved gel stability to an aqueoussolution containing an electrolyte as well as to the body fluids whichis suitable for water-absorbent articles.

These objects as well as other objects and advantages of the presentinvention will become apparent to those skilled in the art from thefollowing description.

SUMMARY OF THE INVENTION

In one aspect of the present invention, there is provided awater-absorbent resin composition which comprises a water-absorbentresin and at least one oxygen-containing reducing inorganic salt. Thiswater-absorbent resin composition of the present invention has animproved gel stability to body fluids such as urine, catamenial blood,secretions and the like.

In another aspect of the present invention, there provides awater-absorbent resin composition which comprises a water-absorbentresin, at least one oxygen-containing reducing inorganic salt and atleast one organic antioxidant. This water-absorbent composition of thepresent invention has an improved stability to an aqueous solutioncontaining an electrolyte in addition to an improved stability to thebody fluids.

In the present invention, although an account of the mechanism of theoxygen-containing reducing inorganic salt and the organic antioxidant inthe water-absorbent resin composition is unclear, properties ofwater-absorbent articles can be remarkably improved simply byincorporation of a small amount of these materials to thewater-absorbent resin without any sanitary problem.

By using the composition of the present invention, there can be obtainedvarious water-absorbent articles having improved properties such asimproved liquid retention characteristics with good prevention of liquidleak and impairment of a feeling in wearing the article. Further, thecomposition of the present invention can be broadly used in the fieldwhere an aqueous solution containing an electrolyte is involved.

DETAILED DESCRIPTION OF THE INVENTION

The water-absorbent resin used in the composition of the presentinvention is not limited to a specific one and any conventionalwater-absorbent resin can be used. Examples of the water-absorbent resininclude crosslinked polyacrylic acid salts, crosslinked copolymers ofvinyl alcohol-acrylic acid salt, crosslinked saponification products ofstarch-acrylonitrile graft copolymer, crosslinked starch-acrylic acidsalt copolymer, crosslinked products of polyvinyl alcohol grafted withmaleic anhydride, crosslinked carboxymethyl cellulose alkali metal saltand the like.

In one aspect of the present invention, the water-absorbent resin isincorporated with the oxygen-containing reducing inorganic salt toimprove its gel stability to body fluids such as urine, catamenialblood, secretions, etc.

As the oxygen-containing reducing inorganic salt in the presentinvention, particularly, there can be used at least one member selectedfrom the group consisting of sulfites, bisulfites, pyrosulfites,dithionites, trithionates, tetrathionates, thiosulfates and nitrites.Specific examples of these oxygen-containing reducing inorganic saltsinclude sulfites such as sodium sulfite, potassium sulfite, calciumsulfite, zinc sulfite, ammonium sulfite, etc.; bisulfites such as sodiumbisulfite, potassium bisulfite, calcium bisulfite, ammonium bisulfite,etc.; pyrosulfites such as sodium pyrosulfite, potassium pyrosulfite,ammonium pyrosulfite, etc.; dithionites such as sodium dithionite,potassium dithionite, ammonium dithionite, calcium dithionite, zincdithionite, etc.; trithionates such as potassium trithionate, sodiumtrithionate, etc.; tetrathionates such as potassium tetrathionate,sodium tetrathionate, etc.; thiosulfates such as sodium thiosulfate,potassium thiosulfate, ammonium thiosulfate, etc.; and nitrites such assodium nitrite, potassium nitrite, calcium nitrite, zinc nitrite, etc.They can be used alone or in combination thereof. Among them, from thesanitary and gel stability points of view, sodium sulfite, sodiumbisulfite, sodium pyrosulfite, sodium dithionite and sodium nitrite arepreferred.

In the present invention, the oxygen-containing reducing inorganic saltis used in an amount of 0.001 to 10 parts by weight, preferably, 0.01 to5 parts by weight per 100 parts by weight of the water-absorbent resin.When the amount of the reducing inorganic salt is less than 0.001 partby weight per 100 parts by weight of the water-absorbent resin,improvement of gel stability of the water-absorbent resin to the bodyfluids is scarcely expected. On the other hand, when the amount is morethan 10 parts by weight, a water-absorption capacity of a resultingcomposition is lowered, while gel stability of the water-absorbent resinto the body fluids is improved.

In another aspect of the present invention, the water-absorbent resin isincorporated with both the oxygen-containing reducing agent and theorganic antioxidant to improve its gel stability to both the body fluidsand an aqueous solution containing an electrolyte such as physiologicalsaline solution, artificial urine and the like.

In this aspect, the above-described oxygen-containing reducing agent canbe used in an amount of the same range as described above in view of gelstability and a water-absorption capacity.

As the organic antioxidant, particularly, there can be used at least onemember selected from the group consisting of ascorbic acid and itsderivatives, gallic acid and its derivatives, benzothiazoles,dithionates, thiurams, benzimidazoles, formaldehyde sulfoxylates andphenothiazines. Specific examples of these organic antioxidant includeascorbic acid and its derivatives such as L-ascorbic acid,sodium-L-ascorbate, isoascorbic acid, sodium isoascorbate, etc.; gallicacid and its derivatives such as gallic acid, methyl gallate, ethylgallate, n-propyl gallate, isoamyl gallate, octyl gallate, laurylgallate, etc.; benzothiazoles such as mercaptobenzothiazole, sodiummercaptobenzothiazole, zinc mercaptobenzothiazole, etc.; dithionatessuch as zinc methyldithiocarbamate, zinc diethyldithiocarbamate, zincdi-n-butyldithiocarbamate, zinc ethylphenyldithiocarbamate, etc.;thiurams such as tetramethylthiuram disulfide, tetraethylthiuramsulfide, tetrabutylthiuram disulfide, tetramethylthiuram monosulfide,etc.; benzimidazoles such as 2-mercaptobenzimidazole, etc.; formaldehydesulfoxylates such as sodium formaldehyde sulfoxylate, etc.; andphenothiazines such as phenothiazine, 2-methoxyphenothiazine, etc. Theycan be used alone or in combination thereof. Among them, from thesanitary and gel stability points of view, L-ascorbic acid, sodiumL-ascorbate, isoascorbic acid, sodium isoascorbate and n-propyl gallateare preferred.

In the present invention, the organic antioxidant is used in an amountof 0.0001 to 10 parts by weight, preferably, 0.001 to 5 parts by weightper 100 parts by weight of the water-absorbent resin. When the amount ofthe antioxidant is less than 0.0001 part by weight per 100 parts byweight of the water-absorbent resin, improvement of gel stability of thewater-absorbent resin to an aqueous solution containing an electrolytesuch as physiological saline solution or artificial urine isinsufficient. On the other hand, when the amount is more than 10 partsby weight, gel stability of the water-absorbent resin becomes inferior.Further, when the water-absorbent resin is incorporated with only theantioxidant without incorporation of the oxygen-containing reducinginorganic salt, gel stability of the water-absorbent resin is ratherlowered and therefore, in the present invention, the antioxidant shouldbe used together with the inorganic salt.

The water-absorbent resin composition of the present invention can beprepared by blending the water-absorbent resin with theoxygen-containing reducing inorganic salt and, if necessary, the organicantioxidant. The blending method is not limited to specific one and anyknown method can be employed. For example, the inorganic salt and theantioxidant can be added to a polymerization reaction mixture of thewater-absorbent resin. Further, they can be blended with the driedwater-absorbent resin by so-called dry blending.

The water-absorbent resin composition of the present invention can beused for the production of various water-absorbent articles according toa conventional method.

The following Preparations, Comparative Examples and Examples furtherillustrate the present invention in detail but are not to be construedto limit the scope thereof.

PREPARATIONS Preparation 1

Cyclohexane (213 g) was placed in a 500 ml four necked round bottomflask equipped with a stirrer, a reflux condenser, a dropping funnel anda nitrogen gas inlet. To the flask was charged sorbitan monolauratehaving HLB of 8.6 (manufactured and sold by Nippon Oil and Fats Co.,Ltd., Japan under the trade name of Nonion LP-20R) (1.9 g). Afterdissolution of the surfactant with stirring at room temperature,dissolved oxygen was purged with nitrogen gas.

Separately, a 80% (w/w) aqueous solution of acrylic acid (48.8 g) wasplaced in a 200 ml conical flask and a 25.9% (w/w) aqueous solution ofsodium hydroxide (66.7 g) was added dropwise with cooling to neutralize80 mole % of the acrylic acid. To the mixture was added potassiumpersulfate (0.13 g).

The resulting partially neutralized acrylic acid solution was added tothe above four necked round bottom flask and the mixture was thoroughlypurged with nitrogen gas. The mixture was heated and subjected topolymerization reaction for 3 hours while maintaining the bathtemperature at 55° to 60° C.

Water and cyclohexane were distilled off and the residue was dried toobtain a fine granular water-absorbent resin (48.5 g).

Preparation 2

n-Heptane (280 ml) was placed in a 500 ml four necked round bottom flaskequipped with a stirrer, a reflux condenser, a dropping funnel and anitrogen gas inlet. To the flask was charged hexaglyceryl monobeheniratehaving HLB of 13.1 (manufacture and sold by Nippon Oil and Fats, Co.,Ltd., Japan under the trade name of Nonion GV-106) (0.75 g). Afterdispersion of the surfactant, dissolved oxygen was purged with nitrogengas. Temperature was raised to 50° C. to dissolve the surfactant andthen the mixture was cooled to 30° C.

Separately, a 80% (w/w) aqueous solution of acrylic acid (37.5 g) wasplaced in a 200 ml conical flask and a 25.4% (w/w) aqueous solution ofsodium hydroxide (49.3 g) was added dropwise with ice-cooling toneutralize 75 mole % of the acrylic acid. To the mixture was addedpotassium persulfate (0.045 g).

The resulting partially neutralyzed acrylic acid solution was added tothe above four necked round bottom flask and the mixture was thoroughlypurged with nitrogen gas. The mixture was heated and subjected topolymerization reaction for 2 hours while maintaining the bathtemperature at 55° to 60° C.

Water and n-heptane were distilled off and the residue was dried toobtain a water-absorbent resin (40.2 g).

Preparation 3

A water-absorbent resin (40.3 g) was obtained according to the samemanner as described in Preparation 2 except that ethylene glycoldiglycidyl ether (0.038 g) was added to the polymerization reactionmixture.

COMPARATIVE EXAMPLES AND EXAMPLES

In the following Comparative Examples and Examples, absorbency,evaluation of gel stability to a saline solution (0.9% (w/w) aqueoussolution of sodium chloride), preparation of an absorbent article andevaluation of gel stability of human urine were carried out as follows.

Absorbency

A water-absorbent resin (1 g) was dispersed in a 0.9% (w/w) aqueoussolution of sodium chloride (200 ml) to thoroughly swell. After 4 hoursor 15 hours, the swollen resin was filtered through a 100 mesh metallicwire gauze and the volume of the swollen resin obtained as a filter cakewas measured and the value was taken as the absorbency.

Evaluation of gel stability to a saline solution

The swollen resin obtained in the above measurement of the absorbencywas pressed with the fingers to organoleptically evaluate its gelstability according to the following four criteria.

A: Gel was not crumbled even by pressing strongly.

B: Gel was crumbled by pressing strongly.

C: Gel was observed but readily crumbled.

D: No gel form was retained.

Preparation of an absorbent article

A pulp having the basis weight of 150 g/m² was cut out to form a sheet(20 cm×10 cm) and a water-absorbent resin or water-absorbent resincomposition (3 g) was uniformly scattered thereon. Further, the samesheet as described above was laminated thereon and pressed by uniformlyapplying a pressure of 1 kg/cm² to obtain an absorbent article.

Evaluation of gel stability to human urine

Human urine (120 ml) was poured on the center part of the above-preparedabsorbent article over 1 minute and the article was allowed to stand for5 minutes. Then, the absorbent article which absorbed human urine waspackaged in a polyethylene bag and the bag was placed in an incubator at37° C. After 4 hours or 15 hours, the absorbent article was taken out ofthe bag and pressed with the fingers to orgnaoleptically evaluate itsgel stability according to the following four criteria.

A: Gel was not crumbled even by pressing strongly.

B: Gel was crumbled by pressing strongly.

C: Gel was observed but readily crumbled.

D: No gel form was retained.

Comparative Examples 1 to 5

By using the water-absorbent resins obtained in the above Preparations 1to 3 and commercially available water-absorbent resins, Arasorb 720(crosslinked polyacrylic acid salt manufactured and sold by ArakawaChemical Co., Ltd., Japan) and Sanwet IM-1000 (crosslinkedstarch-acrylic acid salt graft copolymer manufactured and sold by SanyoChemical Industries Co., Ltd., Japan), the above measurement ofabsorbency, evaluation of gel stability to a saline solution, andevaluation of gel stability to human urine were carried out. The resultsare shown in Table 1.

Comparative Example 6

A water-absorbent resin composition was prepared by thoroughly blendingthe water-absorbent resin power (40.0 g) obtained in the abovePreparation 2 with L-ascorbic acid powder (0.4 g). By using thewater-absorbent resin composition, the above measurement of absorbency,evaluation of gel stability to a saline solution, and evaluation of gelstability to human urine were carried out. However, no desired resultcould not be obtained.

                                      TABLE 1                                     __________________________________________________________________________               Absorbency                                                                    (g/g)    Evaluation of gel stability                                     Water-                                                                             Aqueous  Aqueous                                                   Comp. absorbent                                                                          0.9% NaCl                                                                              0.9% NaCl Human urine                                     Ex. No.                                                                             resin                                                                              4 hrs.                                                                             15 hrs.                                                                           4 hrs.                                                                             15 hrs.                                                                            4 hrs.                                                                             15 hrs.                                    __________________________________________________________________________    1     Prep. 1                                                                            85   85  B    B    D    D                                          2     Prep. 2                                                                            70   70  A    A    C    D                                          3     Prep. 3                                                                            50   50  A    A    B    C                                          4     Arasorb                                                                            62   62  B    B    C    D                                                720                                                                     5     Sanwet                                                                             75   75  B    B    D    D                                                IM-1000                                                                 __________________________________________________________________________

Examples 1 to 24

Various water-absorbent resin compositions were prepared by thoroughlyblending the water-absorbent resins used in the above ComparativeExamples with oxygen-containing reducing inorganic salts in variousratios. By using the water-absorbent resin compositions thus obtained,the above measurement of absorbency, evaluation of gel stability to asaline solution, and evaluation of gel stability to human urine werecarried out. The results are shown in Tables 2A and 2B.

Example 25

A water-absorbent resin composition (40.5 g) was obtained by addition ofsodium sulfite (0.4 g) to the polymerization mixture of the abovePreparation 2. By using the water-absorbent resin composition thusobtained, the above evaluation of gel stability to human urine wascarried out. As the result, both evaluations after 4 hours and 15 hourswere A.

                  TABLE 2A                                                        ______________________________________                                        Water-absorbent resin composition                                                             Oxygen-containing reducing                                    Water-          inorganic salt                                                       absorbent                    Amount*                                   Ex. No.                                                                              resin        Salt            (parts)                                   ______________________________________                                        1      Prep. 1      sodium sulfite  0.5                                       2      Prep. 1      sodium dithionite                                                                             1.5                                       3      Prep. 1      potassium nitrite                                                                             4.0                                       4      Prep. 1      potassium pyrosulfite                                                                         1.5                                       5      Prep. 1      sodium bisulfite                                                                              4.0                                       6      Prep. 2      potassium bisulfite                                                                           0.5                                       7      Prep. 2      sodium nitrite  4.5                                       8      Prep. 2      calcium nitrite 5.0                                       9      Prep. 2      sodium pyrosulfite                                                                            2.0                                       10     Prep. 2      potassium bisulfite                                                                           0.1                                       11     Prep. 3      sodium bisulfite                                                                              1.0                                       12     Arasorb 720  potassium sulfite                                                                             0.5                                       13     Arasorb 720  sodium dithionite                                                                             3.5                                       14     Sanwet IM-1000                                                                             sodium sulfite  0.05                                      15     Sanwet IM-1000                                                                             sodium sulfite  1.0                                       16     Sanwet IM-1000                                                                             sodium sulfite  5.0                                       17     Prep. 1      potassium bisulfite                                                                           5.0                                       18     Prep. 1      sodium dithionite                                                                             1.5                                       19     Prep. 2      sodium sulfite  4.0                                       20     Prep. 2      calcium nitrite 0.5                                       21     Prep. 3      sodium pyrosulfite                                                                            1.0                                       22     Prep. 3      sodium bisulfite                                                                              0.1                                       23     Arasorb 720  sodium sulfite  3.5                                       24     Sanwet IM-1000                                                                             sodium sulfite  2.0                                       ______________________________________                                         Note:                                                                         *parts by weight per 100 parts by weight of the waterabsorbent resin     

                  TABLE 2B                                                        ______________________________________                                        Absorbency**                                                                  (g/g)           Evaluation of gel stability                                   Aqueous         Aqueous                                                       0.9% NaCl       0.9% NaCl    Human urine                                      Ex. No. 4 hrs.  15 hrs. 4 hrs.                                                                              15 hrs.                                                                              4 hrs.                                                                              15 hrs.                            ______________________________________                                        1       --      --      --    --     A     B                                  2       --      --      --    --     A     A                                  3       --      --      --    --     A     A                                  4       --      --      --    --     A     A                                  5       --      --      --    --     A     A                                  6       --      --      --    --     A     A                                  7       --      --      --    --     A     A                                  8       --      --      --    --     A     A                                  9       --      --      --    --     A     A                                  10      --      --      --    --     A     B                                  11      --      --      --    --     A     A                                  12      --      --      --    --     A     B                                  13      --      --      --    --     A     A                                  14      --      --      --    --     B     C                                  15      --      --      --    --     B     B                                  16      --      --      --    --     A     A                                  17      96      32      C     D      A     A                                  18      120     76      C     D      A     A                                  19      78      99      B     D      A     A                                  20      106     53      C     D      A     B                                  21      103     47      C     D      A     A                                  22      55      118     A     C      A     B                                  23      71      95      A     C      A     A                                  24      87      120     B     C      A     A                                  ______________________________________                                         Note:                                                                         **variance in absorbency is larger, gel is more unstable.                

Examples 26 to 28

Various water-absorbent resin compositions were prepared by thoroughlyblending the water-absorbent resins used in the above ComparativeExamples with oxygen-containing reducing inorganic salts and organicantioxidants in various ratios. By using the water-absorbent resincompositions thus obtained, the above measurement of absorbency,evaluation of gel stability to a saline solution, and evaluation of gelstability to human urine were carried out. The results are shown inTables 3A and 3B.

                  TABLE 3A                                                        ______________________________________                                        Water-absorbent resin compostion                                                        Oxygen-containing                                                             reducing                                                            Water     inorganic salt Organic                                              Ex.  Absorbent          Amount*                                                                              antidioxidant                                                                          Amount*                               No.  resin    Salt      (parts)                                                                              Compound (parts)                               ______________________________________                                        26   Prep. 1  potassium 5.0    L-ascorbic                                                                             0.002                                               bisulfite        acid                                           27   Prep. 1  sodium    1.0    L-ascorbic                                                                             0.02                                                sulfite          acid                                           28   Prep. 1  ammonium  2.8    zinc ethyl-                                                                            1.3                                                 pyrosulfite      phenyldithio-                                                                 carbamate                                      29   Prep. 2  sodium    4.0    phenothiazine                                                                          0.8                                                 sulfite                                                         30   Prep. 2  sodium    1.0    n-propyl 5.0                                                 sulfite          gallate                                        31   Prep. 2  calcium   0.5    n-propyl 1.0                                                 nitrite          gallate                                        32   Prep. 2  calcium   4.7    n-propyl 1.0                                                 nitrite          gallate                                        33   Prep. 3  sodium    1.0    mercapto-                                                                              0.3                                                 pyrosulfite      benzothi-                                                                     azole                                          34   Prep. 3  sodium    0.1    2-mercapto-                                                                            0.1                                                 bisulfite        benzimidazole                                  35   Arasorb  potassium 3.5    tetramethyl-                                                                           3.0                                        720      sulfite          thiuram                                                                       disulfide                                      36   Arasorb  sodium    1.1    sodium   4.8                                        720      dithionite       formaldehyde                                                                  sulfoxylate                                    37   Sanwet   sodium    2.0    sodium   0.005                                      IM-1000  sulfite          isoascorbate                                   38   Sanwet   sodium    2.0    sodium   0.1                                        IM-1000  sulfite          isoascorbate                                   ______________________________________                                         Note:                                                                         *parts by weight per 100 parts by weight of the waterabsorbent resin     

                  TABLE 3B                                                        ______________________________________                                        Absorbency**                                                                  (g/g)           Evaluation of gel stability                                   Aqueous         Aqueous                                                       0.9% NaCl       0.9% NaCl   Human urine                                       Ex. No.                                                                              4 hrs.  15 hrs.  4 hrs.                                                                              15 hrs.                                                                             4 hrs.                                                                              15 hrs.                             ______________________________________                                        26     83      83       B     B     A     A                                   27     84      84       B     B     A     A                                   28     85      85       B     B     A     A                                   29     68      68       A     A     A     A                                   30     69      70       A     A     A     A                                   31     70      70       A     A     A     A                                   32     67      66       A     A     A     A                                   33     50      50       A     A     A     A                                   34     50      50       A     A     A     A                                   35     58      57       A     A     A     A                                   36     59      59       A     A     A     A                                   37     74      74       B     B     A     A                                   38     74      74       B     B     A     A                                   ______________________________________                                         Note:                                                                         **variance in absorbency is larger, gel is more unstable.                

As seen from Tables 1, 2A and 2B, the water-absorbent resin compositionof the present invention comprising the water-absorbent resin and theoxygen-containing reducing inorganic salt has superior gel stability tothe body fluid in comparison with the water absorbent resin alone.Further, as seen from Table 1, 3A and 3B, the water-absorbent resincomposition of the present invention comprising the water-absorbentresin, the oxygen-containing reducing inorganic salt and the organicantioxidant has superior gel stability to both the body fluid and anaqueous solution containing an electrolyte in comparison with the waterabsorbent resin alone.

What is claimed is:
 1. A water-absorbent resin composition whichcomprises crosslinked polyacrylic acid salts, crosslinked copolymers ofvinyl alcohol-acrylic acid salt, crosslinked saponification products ofstarch-acrylonitrile graft copolymer, crosslinked starch-acrylic acidsalt copolymer, crosslinked products of polyvinyl alcohol grafted withmaleic anhydride, or crosslinked carboxymethyl cellulose alkali metalsalts and at least one oxygen-containing reducing inorganic saltselected from the group consisting of sulfites, bisulfites,pyrosulfites, dithionites, trithionates, tetrathionates, thiosulfates,and nitrites.
 2. A water-absorbent resin composition according to claim1, wherein the composition contains the oxygen-containing reducinginorganic salt in an amount of 0.001 to 10 parts by weight per 100 partsby weight of the water-absorbent resin.